Beneath the Surface

When seas are rough, gathering coastal water quality data can be a dangerous task for scientists onboard a ship. A collaborative team of researchers has a solution to minimize the risk: a robotic vehicle that will go beneath the surface, efficiently and safely capturing data about coastal water quality.

The robotic vehicle, known as an autonomous underwater vehicle (AUV), even allowed EPA to take ocean samples beneath Hurricane Irene, one of the few times an AUV was able to capture data during such a powerful storm.

"It was gathering data as Hurricane Irene was going over it," said EPA Environmental Scientist, Darvene Adams. "We were able to see how the water column reacts to the storm and how the water gets re-oxygenated by the hurricane. The whole study helps us understand the health of the ocean waters."

This particular AUV, called the "Slocum glider" –which resembles a six foot-long yellow torpedo– made its second summer deployment thanks to a collaborative effort between New Jersey's Department of Environmental Protection, Rutgers University, EPA Region 2 Office (serving New Jersey, New York, the U.S. Virgin Islands and eight Tribal Nations) and the Agency's Office of Research and Development.

Within three miles of shore, the Slocum glider maneuvered more than 185 miles along the New Jersey coastline collecting temperature, salinity, and dissolved oxygen readings. The purpose of the experiment was to check the health of the State's coastal zone during the peak of summer, a time of year when warm surface waters form what scientists call a "thermocline" – a transitional, mixed layer of water separating the warmer surface waters from the colder layers below. Under certain conditions, this layering of the water column can lead to poor water quality and can be harmful to humans and aquatic life.

"We are using the glider as reconnaissance," said Josh Kohut, principal investigator on the project and a physical oceanographer at Rutgers. "It's going out and monitoring dissolved oxygen along the coast during the peak beach season of the summer and relaying back where it's high and where it's low. That data can guide decisions that are being made at the state offices and regional offices of the EPA – whether a response is needed, and how it might be carried out."

"With some modifications, the glider was able to operate in shallow waters at a depth of 25 feet, much shallower than most gliders, which need at least 100 to 1,000 feet to gather data," Kohut said.

Instead of using a propeller, the Slocum glider moves forward by using its fins to steer the craft at an angle like flaps on an airplane wing, riding density gradients in the water up and down. The glider surfaces every two hours to take GPS readings and to send the scientific data back to shore using a satellite telephone connection.

"There's no way to obtain these data otherwise," said Michael Borst, a chemical engineer at EPA. "The alternatives are to moor at many stations off the coast, or people can run out in boats to make measurements. This glider technology efficiently and economically merges these two techniques."